What causes itching?
Pruritus can be caused by many conditions. Stress, anxiety, or other emotional problems can cause itching. Stress also can aggravate itch from other causes. Dry skin (xerosis) is perhaps the most frequent cause of itch without a rash. Many people also report sunburn itch following prolonged exposure to UV radiation from the sun along with the pain of sunburn. Other causes of generalized itching that may not produce a rash or specific skin changes include metabolic and hormone disorders (for examples, kidney disease, hyperthyroidism), cancers (for example, lymphoma), reactions to drugs, interruptions in bile flow (cholestasis) from liver disease, and diseases of the blood (for example, polycythemia rubra vera). Itching is common with allergic reactions, such as food allergies or other types of allergy. Itching can also result from insect stings and bites such as mosquito or flea bites.
Psoriasis is a chronic cause of skin inflammation that can also be associated with itching. Patients with psoriasis typically develop red, elevated, scaling plaques of dry, itchy skin. Atopic dermatitis is a chronic inflammatory disease of the skin that usually starts in childhood. Itching, rash, and thickening of the skin over time are characteristic symptoms of atopic dermatitis. This is considered to be a type of allergy that is associated with inhaled allergies (hay fever) and is chronic.
Infections and infestations of the skin are another cause of itch. Genital itching or anal itching, which may accompany burning and pain, in men and women can occur as a result of genital infections such as sexually transmitted diseases (STDs). Vaginal itching is sometimes referred to as feminine itching, and sexually transmitted diseases can also cause anal itching and pain. Vaginal yeast infections are another cause of vaginal itching. Other common infectious causes of itch include a yeast (fungal) infection of the crotch (tinea cruris) commonly known as jock itch, psoriasis, and ringworm of the body (tinea corporis). Another type of parasitic infection resulting in an itchy sensation is the so-called swimmer's itch. Swimmer's itch, also called cercarial dermatitis, is a skin rash caused by an allergic reaction to infection with certain parasites of birds and mammals that are released from infected snails in fresh and saltwater. Itch may also result from skin infestation by body lice, including head lice and pubic lice. Scabies is a highly contagious skin condition caused by an infestation by the itch mite Sarcoptes scabiei that is known to cause an intense itch that is particularly severe at night.